Referring to FIGS. 9 and 10, a semiconductor wafer 40 of, for example, silicon or gallium arsenide is produced in the form of a disk having a large diameter. This semiconductor wafer 40 is stuck through a pressure sensitive adhesive sheet 41 onto a ring frame 42. Subsequently, the semiconductor wafer 40 is cut apart into a multiplicity of dice formed chips 44 (dicing) by the use of a dicing saw 43. In this state, the semiconductor wafer is transferred to the subsequent steps such as cleaning, drying and die bonding steps. In this process, after the completion of the dicing step, the pressure sensitive adhesive sheet 41 is drawn outward by appropriate means so that the spacings of the mutually neighboring chips 44 are expanded.
It is desired that the conventional pressure sensitive adhesive sheet 41 have satisfactory adhesive strength to the chips 44 from the dicing step in which the wafer is cut apart into dice formed chips through the drying step. Further, referring to FIG. 11, it is desired that, in picking up the chips from the pressure sensitive adhesive sheet 41, the adhesive strength be such that no residue of pressure sensitive adhesive is attached to the chips 44.
Various pressure sensitive adhesive sheets of the above type have been proposed in, for example, Japanese Patent Laid-open Publication Nos. 60(1985)-196956 and 60(1985)-223139. Further, in recent years, pressure sensitive adhesive sheets in which a UV curable pressure sensitive adhesive is used for reducing the adhesive strength at the time of pick-up have been proposed. However, the conventional pressure sensitive adhesive sheets 41 have a drawback in that, in the use thereof, it is difficult to realize uniform spacings between the chips 44 at the stage of expanding the chip spacings, thereby causing a spacing dispersion, with the result that the processing at each step encounters disorders. Further, bringing the adhesive strength at pick-up (vertical peeling strength) to complete nil is practically unfeasible, and the reduction of the vertical peeling strength at pick-up has encountered a limit of about 100 to 300 g/10 mm.sup.2. Therefore, at the die bonding step at which a pick-up is carried out, the pressure sensitive adhesive sheet 41 must be forcibly pushed up from the back thereof with the use of a push-up needle 45. Therefore, there are disorders such as damaging of the chips 44 or migration of, for example, the pressure sensitive adhesive which adheres to the push-up needle 45 to the back of the chips 44.
Still further, the pressure sensitive adhesive sheet in which a UV curable pressure sensitive adhesive is used has not yet reached a stage such that all the chips 44 can be peeled without the need to use the push-up needle 45. The present applicants have proposed a technique in which the area of adhesion and the adhesive strength between the chips and the sheet are reduced by the use of a shrink film which can be shrunk by heating in place of the pressure sensitive adhesive sheet in which a UV curable pressure sensitive adhesive is used.
The present invention has been made with a view toward resolving the above problems of the prior art. The present invention provides a method of die bonding electronic components, in which use is made of a shrink film capable of expanding the chip spacings by a mechanism that is radically different from that of the conventional expansion method to thereby enable effective bonding without damaging the chips. The present invention also provides a die bonding apparatus therefor.